1. Field
The present invention relates to micro LED devices. More particularly embodiments of the present invention relate to a method and structure for integrating micro LED devices on a substrate with a tunable color emission spectrum.
2. Background Information
Quantum dots are semiconductor nanocrystals that can be tuned to emit light throughout the visible and infrared spectrum. Due to the small size of 1 to 100 nm, more typically 1 to 20 nm, quantum dots display unique optical properties that are different from those of the corresponding bulk material. The wavelength, and hence color, of the photo emission is strongly dependent on the size of a quantum dot. For an exemplary cadmium selenide (CdSe) quantum dot, light emission can be gradually tuned from red for a 5 nm diameter quantum dot, to the violet region for a 1.5 nm quantum dot. There are generally two types of schemes for quantum dot (QD) excitation. One uses photo excitation, and the other uses direct electrical excitation.
One proposed implementation for quantum dots is integration into the backlighting of a liquid crystal display (LCD) panel. Current white light emitting diode (LED) backlight technology for LCD panels utilizes a cerium doped YAG:Ce (yttrium aluminum garnet) down-conversion phosphor layer over a plurality of blue emitting LED chips. The combination of blue light from the LED chips and a broad yellow emission from the YAG:Ce phosphor results in a near white light. It has been proposed to replace the YAG:Ce phosphor with a blend of quantum dots to achieve the white backlighting.
Another proposed implementation for quantum dots is a quantum dot light emitting diode (QD-LED). The structure of the QD-LED is similar to that of the organic light emitting diode (OLED), with the major difference being that the organic emission layer from the OLED technology is replaced with a quantum dot film between a hole transporter layer and an electron transporter layer. Once an electric field is applied, the electrons and holes move into the quantum dot film, where they are captured in the quantum dots and recombine, emitting photons.